1. Field of the Invention
The present invention relates to a surface light emitting apparatus that uses a plurality of light sources, and, more particularly, to a surface light emitting apparatus having a relatively large area of light emitting surface.
2. Description of the Related Art
Liquid crystal display apparatuses are commonly used in portable electronic devices and various image display apparatuses today. The liquid crystal display apparatus is constituted from liquid crystal cell, prism sheet, a diffusion sheet, a backlight and other major components. For the backlight source, LED, cold cathode tube or the like is used. Different types of backlight source have their own features and are selected according to the application. For example, a backlight source employing the cold cathode tube is used in a relatively large liquid crystal display apparatus, and a backlight source employing the LED is used in a small liquid crystal display apparatus of cellular phones.
All of these backlight sources employ an optical guide plate, whereby light emitted by a cold cathode type fluorescent lamp used as a linear light source or a light emitting diode used as a point light source is diffused over the entire light emitting surface, thereby to effect surface light emission. Various techniques have been developed in order to achieve uniform luminance over the entire light emitting surface.
However, the optical guide plate that is an inevitable component of the backlight source has been hindering the efforts to reduce the weight and/or depth of the backlight source for relatively large liquid crystal display apparatuses.
Against this background, a backlight source that has a hollow space through which light is guided, without employing any optical guide plate has been developed (refer to FIG. 13 and FIG. 14 of Japanese Unexamined Patent Publication No. 2003-57622).
However, in case surface light emission is attempted with light emitted by a point light source or a linear light source without using an optical guide plate, such a problem arises as luminance distribution over the light emitting surface has unevenness, thus resulting in poor uniformity of light emission.
This problem becomes conspicuous particularly when a point light source consisting of light emitting diode is used as the light source.